I have a macbook pro 13" late 2011 with OSX 10.7.5 and does not connect automatically to a known Wi-Fi network after waking from sleep. I found an update to solve this problem, but is for 10.7.3 and does not work for me. Help!!
Did you check keychain if you do not have multiple entries for the same WiFi network? This often is a problem.
If so disconnect WiFi delete all keys in Keychain refering to this SSID and connect again.
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